One Saturday morning last September, an elevator door opened and half a dozen elite runners spilled into the lobby of the Warwick Hotel, in Midtown Manhattan. They wore tracksuits and clean white sneakers and had iPod buds stuck in their ears, and they were greeted by coaches, handlers, or parents who'd been milling around the lounge waiting to escort them to the start of the Fifth Avenue Mile.

Jammed in among them was 25-year-old Alan Webb, the best middle-distance American runner to come along in a generation. Two months earlier, Webb had run a mile in 3:46.91, setting a new U.S. record that made him the eighth-fastest miler in history. He'd clocked 2007's best times in both the mile and the 1,500 meters (the metric version of the mile, which is the standard at most international races) and the second-best time in the 800. The Fifth Avenue Mile would be his final race of the season, and Webb was favored to win. But if he'd learned anything as a professional runner, it was to not take winning for granted.

At five-nine and 145 pounds, Webb has a wiry, toned build, an eagle's beak, and ears so big you'd think they must flap when he runs. His face was still and blank, except for his eyes, which flicked back and forth like a cat's as he scanned the room for his coach, Scott Raczko. Once Webb spotted him, he parted the crowd with the practiced aloofness of a weary celebrity, ignoring race handlers and well-wishers. Together they walked through the doors and into the day.

It was a perfect morning for racing, sunny and still cool at 10 o'clock, with marshmallow clouds drifting into view in the gaps between apartment buildings. On the course, which stretched from 80th Street to 60th Street, runners had been streaming south all morning. This was mostly an amateur contest, drawing more than 3,200 recreational athletes, but Webb and ten other professionals were lured by the high-profile venue, sizable appearance fees, and a $32,000 purse. They would race last.

Webb's mother, Kathy, had staked out a front-row spot near the finish; behind her, his dad, Steve, paced the sidelines. (Webb's expanded posse, not all present today, also includes Raczko, a media-averse agent named Ray Flynn, and, of late, his girlfriend of six months, 25-year-old Julia Rudd, another elite runner.) His parents couldn't see Webb as the racers spread out along the start line, 20 blocks to the north, shaking out their limbs and double-knotting their shoelaces. Nor could they hear the gun go off or the slap of rubber soles as the runners jockeyed for position inside the pack. It didn't much matter: In three minutes and 45 seconds, the pros would be in sight, and about eight seconds after that it would all be over.

"This is it, New York!" the announcer yelled as the leaders appeared on the empty avenue, just wiggly dots at first but growing with each step into recognizable humans, arms and legs chugging efficiently. "With under 20 meters to go, Alan Webb goes into the lead! Alan Webb is going to win New York!"

"Go, Alan, go, go, go, go, go!" Kathy shrieked, louder and louder until she was howling unintelligibly. Webb was in front, arms outstretched, flimsy shorts fluttering in the breeze. The runners seemed to move forward in slow motion, their strides long and confident and exaggerated. There was no jostling or lurching, and no one was grimacing, contorting their skeletal bodies in regrettable ways, or, it seemed, even breaking a sweat. Moments later, Webb arched gracefully into the winner's tape. It was over almost before it began. He had just run a mile in 3:52.7, and he made it look easy.

If only things were always this simple. But in a sport where the difference between first and last place can come down to tenths of a second, Webb has been excruciatingly slow in living up to his potential. Ever since he broke Jim Ryun's long-standing high school mile record, in 2001, Webb's career has been clouded by inconsistency, from a troubled NCAA stint to a rough transition to the pro ranks and a disappointing finish at the 2004 Olympics, in Athens. While last season was undoubtedly his best, he's performed unremarkably at his first few races this year. And with the ten-day 2008 Olympic track-and-field trials starting June 27, and spots for only three middle-distance runners on the U.S. team, it's still an open question whether Webb will make the cut. His superstar status—not to mention his $250,000-a-year sponsorship contract with Nike, which comes up for renewal this year—is hanging in the balance.

Granted, Webb has been saddled with some pretty high expectations since the day, seven years ago, he showed up at the annual Prefontaine Classic, in Eugene, Oregon, and ran a mile in 3:53.43, blasting Ryun's high school record, set in 1965, by nearly two seconds and his own personal best by six. Overnight, the 18-year-old from Reston, Virginia, became a media sensation, fawned over by David Letterman and crowned the fleet-footed prodigy who would bring American running a level of success not seen since the 1970s and early 1980s. Those were the sport's golden years, when homegrown idols such as Steve Prefontaine set the U.S. 5K record (1974) and Steve Scott ran a 3:47.69 mile (1982), a national record that stood until Webb came along. Thanks to Webb's rapid rise, the future of an entire, faltering sport was placed squarely on his bony shoulders. But then he shanked.

That fall, on a running scholarship at the University of Michigan, Webb overtrained, injured his Achilles, and flailed on the NCAA circuit. "The media attention was too much," says Webb. "As if I didn't have enough on my plate, just being a normal college freshman away from home for the first time." Though Webb was clearly the Wolverines' hotshot new recruit, Michigan coach Ron Warhurst, a revered figure in the NCAA who has helped 11 track stars win national titles, didn't play favorites. The lack of personalized attention from Warhurst—whom Webb describes as "a lot more hands-off" than his high school coach, Raczko—took its toll. "I wanted to do so well that I pushed every single day—hard, hard, hard—and I just killed myself," Webb says. "I didn't know when to back off, because Ron wasn't telling me to back off."